This invention relates to an ambient pressure sensor for providing an electrical signal which varies in response to changes in ambient pressure level.
Modern automobiles, particularly those which include electronic fuel management systems or which include relatively complicated pollution control mechanisms, require a device which generates an electrical signal which varies as a function of the ambient pressure level. Prior art devices of this type generally provide a potentiometer which is actuated directly by an aneroid to thereby directly generate an electrical signal which varies as a function of the pressure level sensed by the aneroid. However, the forces generated by aneroids are relatively small, and considerable inaccuracies have been experienced in using the prior art devices. These inaccuracies are, in part, due to a reduction in the drag on the potentiometer as the wiper used within the potentiometer and which is moved by the aneroid "beds in". The device of the present invention, which is primarily intended for automotive applications, overcomes the difficulties inherent in the prior art devices by using engine manifold vacuum to actuate the potentiometer shaft to thereby change the electrical output of the potentiometer. The manifold vacuum operates a fluid motor attached to the potentiometer shaft, and the fluid pressure level communicated to the fluid motor is adjusted as a function of the pressure level sensed by the aneroid. Therefore, a much larger force is available to actuate the potentiometer shaft, thereby avoiding the difficulties of the prior art in which the limited force output of the aneroid was often insufficient to actuate the potentiometer.